Luxury hotelier Mandarin Oriental has removed malicious software that was used to steal credit card data from some of its hotels in the U.S. and Europe, the company said.

The security codes for the cards were not compromised, it said Thursday, although it wasn't clear if that referred to the cards' PIN (personal identification number) or the three-digit CVV code on the back. No other personal information was taken, the company said in a statement.

An investigation is underway by law enforcement and forensic specialists. An "isolated number of hotels in the U.S. and Europe were affected," but none in Asia, the company said.

The hotel chain said the malicious software had been "undetectable by all anti-viral systems." Officials could not immediately be reached for further comment.

The retail industry has been battling an increase in attacks that extract card data from payment systems. Retailers are required by credit card companies to follow the PCI Data Security Standard (PCI-DSS), a set of guidelines for handling card data securely.

But criminals have exploited a hole where payment card details are briefly stored unencrypted in a computer's RAM and can be recovered. That type of malware collects the card details after a card has been swiped.

Although security products are updated to detect POS malware, cybercriminals often change its code to evade antivirus scanners. Retailers including Home Depot and Target have experienced large leaks of payment card that have been attributed to point-of-sale (POS) malware.